The present invention relates to oilfield tubulars of the type subjected to high torsion and/or bending forces. More particularly, the present invention relates to an improved drilling connector with a low stress flex groove. The present invention is particularly well suited for oilfield casing drilling tubulars connected by threaded couplings to serve as the drill string, but may also may be used with a pin-in-box oilfield drilling casing to serve as the drill string.
Because many of the known oil and gas fields in the world that are economical to drill with traditional methods have already been developed, new methods are needed that cost less so that the additional fields can be economically developed. One of the most important current developmental efforts being evaluated by operators includes drilling a well using the casing as the drill string, instead of using both casing and drill pipe. This method may save significant time and drill pipe costs and may make a large number of fields economically justified that are currently not justified using traditional methods.
New techniques have also been developed that allow the operator to drill the well without traditional drill pipe by attaching a downhole mud motor with a drill bit to the bottom of the casing. The mud motor thus rotates the drill bit. However, this method generally requires expensive downhole assemblies, including the mud motor. Also, if the drill string is not rotating, the efficiency by which the cuttings are circulated to the surface is reduced.
The present invention allows the operator to rotate the drill bit by rotating the casing. This idea, while not novel, is practically manifested in the drilling connector of the present invention. According to the present invention, the casing thus may completely eliminate the drill pipe, possibly also with enhancement in the retrieval of cuttings. Moreover, the drilling connector of the present invention eliminates the need for a mud motor and other associated equipment, thereby saving additional expenditures and reducing the complexity of the recovery system.
A primary objective of this invention is to increase the fatigue resistance of typical connectors (e.g., low cost API connector designs) subject to high bending and/or torsional forces. This objective allows the tubular casing to be economically used as the drill string, which has long been desired by those skilled in the art.
It is a further objective of this invention to provide a drilling connector with a high resistance to torsional loads created while drilling with the casing.
It is a further objective of this invention to minimize the stresses in the areas of the drilling connector that are most likely to suffer fatigue failures upon torsion and/or bending.
It is a feature of this invention to incorporate a long, gradual bevel on the OD of the drilling connector coupling that will minimize the stress in the casing near the end of the coupling. Abrupt changes in stiffness in any mechanical part of the connector are reduced or eliminated, thereby decreasing stresses and stress risers.
It is also a feature of this invention to allow an improved oilfield tubular that may be upset (forged) on one or both ends, which would eliminate the need for a coupling.
It is a further feature of this invention to provide a drilling connector that incorporates a torque shoulder at the outermost location for the casing joint that has been upset on both ends.
It is a feature of this invention the threads at the base of the pin run-out on the exterior surface of the threaded end of the pin (casing). As the threads approach the O.D., the threads xe2x80x9crun-outxe2x80x9d to reduce stress in that area of the connection.